The present invention relates to a seat belt retractor having a force limiter comprising a deformable material.
DE 44 26 479 C2 teaches a seat belt retractor wherein in a vehicle crash the pressure of the seat belt on the forward-displaced body of the strapped-in vehicle occupant is reduced by the force limiter, as a limited extraction of the belt webbing is made possible with the consumption of energy.
A force limiter in the form of brake discs is known from DE-OS 19 40 867, wherein the braking force can be adjusted by means of an adjusting device as a function of the body weight of the strapped-in vehicle occupant.
There is provided in accordance with the present invention a belt retractor of the type described at the beginning in which an automatic adjustment of the force limiting effect is achieved with little expenditure as a function of the data concerning the vehicle occupant and of the respective crash severity. An inertial mass can be coupled to the second reel part for entrainment by a coupling which is engaged upon blocking of the first reel part and rotation of the second reel part. The inertial mass can be mounted so as to be linearly or rotatably moveable for entrainment.
Preferably step-up gearing can be provided between the second reel part, rotatable upon energy consumption by the force limiter, and the inertial mass. As a result, the effect of the inertial mass on the belt reel can be increased. The inertial mass can be coupled directly via the coupling or via the force limiter to the second reel part. Preferably the force limiter is a torsion bar. To this end, the torsion bar can extend in known manner into the axis of the belt reel, which is hollow on the inside. The force limiter can also be present in the form of friction linings (DE 196 40 842 C2 or DE 197 31 689 C2).
Preferably the force limiter function imparted by the force limiter is designed for a fifth percentile woman. In the crash severity spectrum arising in practice, the lowest rotational speed of the rotatable belt reel part is brought about by such a person strapped in, upon forward displacement in dependence on the respective crash severity. If the person strapped in is of larger dimensions with regard to body weight and body size, corresponding for example to the norm approximately of a 50th percentile man or more (up to a 95th percentile man), the rotational speed of the rotatable reel part will be greater upon forward displacement with the same degree of crash severity. Accordingly, the inertial mass coupled via the coupling acts with increasing inertial force as a reaction force on the rotating reel part or the torsion bar connected to this reel part in the sense of a variable braking force, which is being added thereto.
A self-adjusting influencing of the effect of the force limiter is therefore achieved by the invention from the body data of the person strapped in and the crash severity.